An overview of mark-whole-buffer

In GNU Emacs 22, the code for the complete function looks like this:

(defun mark-whole-buffer ()
"Put point at beginning and mark at end of buffer.
You probably should not use this function in Lisp programs;
it is usually a mistake for a Lisp function to use any subroutine
that uses or sets the mark."
(interactive)
(push-mark (point))
(push-mark (point-max) nil t)
(goto-char (point-min)))

Like all other functions, the mark-whole-buffer function fits
into the template for a function definition. The template looks like
this:

Here is how the function works: the name of the function is
mark-whole-buffer; it is followed by an empty argument list,
‘()’, which means that the function does not require arguments.
The documentation comes next.

The next line is an (interactive) expression that tells Emacs
that the function will be used interactively. These details are similar
to the simplified-beginning-of-buffer function described in the
previous section.